1. Field of the Invention
The present invention relates to a scanning-type exposure apparatus for scanning a mask (or a reticle) and a substrate synchronously to transfer a pattern of the mask to the substrate in a photolithography process for manufacturing, e.g., a semiconductor, a liquid crystal display device or a thin film magnetic head and more particularly to an exposure apparatus of a step-and-scan system for transferring a pattern of a mask to each of a plurality of shot areas on a substrate successively on a scanning exposure system.
2. Related Background Art
In a photolithograpy process for manufacturing a semiconductor or the like, a projection-type exposure apparatus is utilized in which the image of a pattern on a mask or a reticle (hereinafter referred to as the reticle) is transferred via a projection optical system to a photosensitive substrate (a wafer or glass plate with photoresist applied thereto). Recently, the sizes of semiconductors tend to be large and in projection-type exposure apparatuses, it is required to transfer a much larger pattern on a reticle to a photosensitive substrate.
Then, for example, scanning-type exposure apparatuses have been developed in which a reticle and a wafer are scanned synchronously with respect to a rectangular, circular arc or hexagonal illumination area (hereinafter referred to as the slit-like illumination area) to transfer a pattern larger than the slit-like illumination area to the wafer. Such apparatuses are disclosed in e.g., U.S. Pat. Nos. 4,747,678, 4,924,257, 5,194,893, 5,281,996, 5,227,839 and 5,255,051.
Particularly, in scanning and exposing a pattern on a reticle to each of a plurality of shot areas on a wafer, after an exposure for the first shot area has been completed, the stepping of the wafer is carried out so as to position the following shot area to a scanning start position. This system of repeating the stepping and the scanning exposure is called a step-and-scan system. The system of scanning the reticle and the wafer synchronously so as to transfer the pattern of the reticle to the wafer including the step-and-scan system is called "the scanning exposure system" hereinafter.
There are reticles in which each pattern area has a plurality of identical (or different) chip patterns. In this case, when carrying out scanning exposure by means of a stepper adopting a batch exposure processing system, the image of the whole patterns on such a reticle is projected even to each of shot areas located in the periphery of the wafer to which only a portion of the plurality of patterns can be projected (hereinafter referred to as the incomplete shot areas).
When transferring a plurality of chip patterns on a reticle to each of incomplete shot areas on a wafer on the scanning exposure system, the reticle and the wafer are scanned for length (the length of the full field) the same as when the whole chip patterns on the reticle are transferred to the wafer. Therefore, unnecessary portions of the incomplete shot areas (e.g., the peripheral end portion of the wafer) are exposed also. Therefore, time is wasted for scanning the unnecessary portions, which causes the exposure time per shot to become long. As a result, the throughput is lowered.